The amount of data transferred among electronic devices has been increasing rapidly over the years, and this rate of increase shows no signs of abating. In particular, the amount of data transferred by servers, routers, and backplanes has exploded with the increase in popularity of on-demand video and other such data-intensive applications. Present devices are struggling to keep pace with this increase in data traffic. Accordingly, new devices are being developed that will be better able to cope with these high volumes. One aspect of this is the desire to increase the rate of data transfers between these devices.
Currently, data is typically transferred among devices using non-return to zero (NRZ) signaling. Typical data rates may be in the 5-10 Gbps range, with a 10-20 GHz clock frequency. But now engineers are looking for solutions that would be capable of transferring data at the 50 to 100 Gbps range and beyond.
Unfortunately, NRZ signaling does not appear to be suitable at these higher rates. When an NRZ binary signal is passed through a channel having low-pass characteristics, the resulting signal may have excessive attenuation at its high-frequency components, which may lead to increased noise and inter-symbol interference (ISI), thereby making data recovery more difficult.
For these reasons, alternate encoding schemes are being explored, such as Pulse-amplitude modulation (PAM) or duobinary encoding schemes. But these methods of encoding still have speed limitations and have drawbacks of their own such as increase in circuit complexity to implement. For example, decoding of these signals may need to be done using a digital-signal processor (DSP) or other area and power intensive circuits. Moreover, the transmitter and receiver circuitry for these implementations may require large bandwidths and a corresponding increase in power dissipation.
Thus, what is needed are systems, methods and apparatus for transferring data at a high rate where the transmitting and receiving, as well as the encoding and decoding can be done in a space and power efficient manner.